1. Field of the Invention
The present invention relates to a stroke sensor that senses a linear displacement amount (i.e., stroke amount) of a sensed body, which is displaced linearly, and to a rotation angle sensor that senses a rotation angle of a sensed body, which rotates.
2. Description of Related Art
Conventionally, many output values of stroke sensors and rotation angle sensors are used for various types of control of a vehicle and occupy important places in the control. For example, the stroke sensor has a movable member, which forms a magnetic flux and which is displaced linearly in accordance with linear displacement of a sensed body, and a fixed member, which senses the magnetic flux and converts the magnetic flux into an electric output for outputting the electric output. For example, the rotation angle sensor has a movable member, which forms a magnetic flux and which rotates in accordance with rotation of the sensed body, and a fixed member, which senses the magnetic flux and converts the magnetic flux into an electric output for outputting the electric output.
The stroke sensor and the rotation angle sensor calculate respective output values based on the electric outputs outputted from the respective fixed members. An electronic control unit (ECU) grasps a stroke amount and a rotation angle of the sensed body based on the output values and performs various kinds of control processing.
The magnetic flux formed by the movable member and the electric output outputted from the fixed member fluctuate in accordance with temperature. Therefore, sensing accuracy of the stroke sensor and the rotation angle sensor cannot be improved more than a limit based on the temperature characteristics. Therefore, in the stroke sensor, a correlation between the stroke amount and the output value does not become an ideal linear characteristic. In the rotation angle sensor, a correlation between the rotation angle and the output value does not become an ideal linear characteristic, either.
There is proposed a position sensor that forms a magnetic flux with two magnets having different polarities and forms a reversed magnetic flux with another two magnets, whereby the position sensor can obtain output values on both plus side and minus side across zero (for example, refer to Patent document 1: JP-A-2004-286017). However, the magnetic flux and the electric output fluctuate in accordance with the temperature also in the position sensor. The sensing accuracy does not improve more than the limit based on the temperature characteristics. If the magnet rotates while being displaced linearly, the sensed magnetic flux density fluctuates. Therefore, a sensing error of the stroke amount accompanying the rotation of the magnet increases.